The present invention relates to a copolyester, and in particular to a block copolyester.
A known category of thermoplastic elastomers is polyester elastomers, which can be used in a wide range of applications such as in tubes, belts, or molded articles, made for example by injection molding. Such polyester elastomers normally contain a rigid, crystalline polyester (or xe2x80x9chardxe2x80x9d segment), usually an aromatic polyester such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), which is modified with a non-crystalline material (or xe2x80x9csoftxe2x80x9d segment). The hard, crystalline segments are chemically linked with the soft, non-crystalline segments in a single polymeric chain. In this material, the hard segments congregate to form crystalline areas that provide strength and hardness to the material. Similarly, the soft segments congregate in a separate phase, and provide flexibility to the material. PBT is the most commonly used hard segment, because of its ease of crystallization. The soft segment is normally a polyether such as polytetramethylene glycol (PTMEG), polyethyleneglycol (PEG), polypropylene glycol (PPG), or ethylene oxide/propylene oxide block copolymers. The disadvantages of polyethers include their sensitivity to heat, oxidation and UV. Alternative soft segments include aliphatic polyesters such as adipate ester or polycaprolactone, which can be sensitive to hydrolysis. In addition, transesterification tends to occur during synthesis, which results in break up of the hard and/or soft segments with a consequential loss of the required properties. In particular, there is a requirement for a copolyester which possesses both high melting point and low glass transition point.
U.S. Pat. No. 4,031,165-A claims a process of making block copolyesters in the presence of a titanium-type catalyst and a phosphorus compound.
GB-2203425-A is directed to dimerised fatty acids and describes forming polyesters using such dimerised fatty acids. The polyesters produced according to the teaching of GB-2203425-A are homo polyesters or random copolyesters.
JP-11080336-A discloses a copolyester having a non-crystalline part formed from dimer acid, terephthalic acid and polyoxyethylene glycol, and a crystalline part formed from butylene terephthalate.
We have now surprisingly discovered a block copolyester which reduces or substantially overcomes at least one of the aforementioned problems.
Accordingly, the present invention provides a block copolyester comprising a hard segment and a soft segment wherein the melting point of the copolyester is greater than or equal to 200xc2x0 C., and the glass transition temperature of the copolyester is less than or equal to xe2x88x9240xc2x0 C.
The invention also provides a block copolyester comprising a hard segment and a soft segment wherein the melting point of the copolyester is less than 20xc2x0 C. lower than the melting point of the hard segment, and the glass transition temperature of the copolyester is less than 20xc2x0 C. higher than the glass transition temperature of the soft segment.
The invention further provides a method of preparing a block copolyester as defined herein wherein the soft segment is formed in situ, in the presence of the preformed hard segment, and the same diol is used to form both the hard and soft segments.
The composition of the polyester hard segment may vary over a wide range. The polyester is preferably an aromatic polyester. Suitable aromatic dicarboxylic acids, and/or ester derivatives thereof, for use in forming the hard segment, include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, or mixtures thereof. Terephthalic acid, and/or ester derivative thereof, is particularly preferred. The hard segment is preferably formed from greater than 50, more preferably greater than 70, particularly greater than 90, and especially greater than 95 and up to 100 mole % of aromatic dicarboxylic acid(s) and/or ester derivatives thereof. The balance (up to 100 mole %) of dicarboxylic acids (if any) can be suitably made up of aliphatic dicarboxylic acids, such as adipic acid, sebacic acid, or cyclohexane dicarboxylic acid.
Suitable diols or glycols for use in forming the hard segment include aliphatic diols such as ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, trimethylene glycol, tetramethylene glycol, and cyclohexane dimethanol, or aromatic diols such as 2,2-bis(4-hydroxyphenyl)propane. The hard segment is preferably formed from greater than 50, more preferably greater than 70, particularly greater than 90, and especially greater than 95 and up to 100 mole % of aliphatic glycol(s), preferably ethylene glycol and/or 1,4-butanediol.
In a particularly preferred embodiment of the invention, the hard segment is polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate or mixtures thereof, and especially polybutylene terephthalate.
The hard segment preferably has a molecular weight number average in the range from 1000 to 30,000, more preferably 2,000 to 15,000, particularly 2,500 to 10,000, and especially 3,000 to 5,000.
The hard segment preferably has a melting point (Tm) in the range from 200 to 280xc2x0 C., more preferably 210 to 270xc2x0 C., particularly 215 to 255xc2x0 C., and especially 220 to 230xc2x0 C.
The polyester soft segment is preferably an aliphatic polyester. The polyester is preferably formed from a dimer fatty acid and/or ester derivative thereof and/or dimer fatty diol.
The term dimer fatty acid is well known in the art and refers to the dimerisation product of mono- or polyunsaturated fatty acids. Preferred dimer acids are dimers of C10 to C30, more preferably C12 to C24, particularly C14 to C22, and especially C18 alkyl chains. Consequently, preferred dimer acids comprise in the range from 20 to 60, more preferably 24 to 48, particularly 28 to 44, and especially 36 carbon atoms. Suitable dimer fatty acids include the dimerisation products of oleic acid, linoleic acid, linolenic acid, palmitoleic acid, elaidic acid, or erucic acid. The dimerisation products of the unsaturated fatty acid mixtures obtained in the hydrolysis of natural fats and oils, e.g. sunflower oil, soybean oil, olive oil, rapeseed oil, cottonseed oil and tall oil, may also be used.
In addition to the dimer fatty acids, dimerisation usually results in varying amounts of oligomeric fatty acids (so-called xe2x80x9ctrimerxe2x80x9d) and residues of monomeric fatty acids (so-called xe2x80x9cmonomerxe2x80x9d), or esters thereof, being present. The amount of momomer can, for example, be reduced by distillation. Particularly preferred dimer fatty acids have a dicarboxylic (or dimer) content of greater than 95%, more preferably greater than 97.5%, particularly greater than 98.5%, and especially greater than 99.0% by weight.
The soft segment is preferably formed from greater than 50, more preferably greater than 70, particularly greater than 90, and especially greater than 95 and up to 100 mole % of dimer fatty acids and/or ester derivatives thereof. The balance (up to 100 mole %) of dicarboxylic acids (if any) can be suitably made up of non-dimeric fatty dicarboxylic acids and/or ester derivatives thereof. Preferred materials are linear dicarboxylic acids having terminal carboxyl groups having a carbon chain of from 6 to 20, more preferably 8 to 12 carbon atoms, such as adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, heptane dicarboxylic acid, octane dicarboxylic acid, nonane dicarcoxylic acid, decane dicarboxylic acid, undecane dicarboxylic acid, dodecane dicarboxylic acid and higher homologs thereof.
Suitable diols include those mentioned above, and at the same concentration ranges, for forming the hard segment. Alternatively, dimer fatty diols may be used, which can be produced by hydrogenation of the corresponding dimer acid. Thus, the soft segment is preferably formed from greater than 25, more preferably greater than 35, particularly greater than 45, and especially greater than 47.5 and up to 50 mole % of dimer fatty acids or dimer fatty alcohols, or a mixture thereof, based on the total amount of dicarboxylic acids and/or ester derivatives thereof, and diols used to form the soft segment.
The soft segment of the copolyester according to the present invention preferably comprises at least one, more preferably in the range from 1 to 20, more preferably 1 to 15, particularly 2 to 10, and especially 2 to 5 ester bonds.
The soft segment preferably has a glass transition temperature (Tg) in the range from xe2x88x9280 to xe2x88x9240xc2x0 C., more preferably xe2x88x9275 to xe2x88x9245xc2x0 C., particularly xe2x88x9270 to xe2x88x9250xc2x0 C., and especially xe2x88x9265 to xe2x88x9255xc2x0 C.
The soft segment preferably has a molecular weight number average in the range from 500 to 7,500, more preferably 700 to 5,000, particularly 900 to 2,500, and especially 1,000 to 1,500.
The ratio of hard to soft segment present in the block copolyester is preferably in the range from 1 to 20:1, more preferably 2 to 15:1, particularly 3 to 10:1, and especially 4 to 6:1 by weight %.
The block copolyester preferably comprises in the range from 1 to 35, more preferably 2 to 20, particularly 3 to 10, and especially 4 to 6 separate blocks of both hard and soft segment. The copolyester preferably has a molecular weight number average in the range from 5,000 to 100,000, more preferably 15,000 to 80,000, particularly 25,000 to 60,000, and especially 30,000 to 40,000.
The block copolyester preferably comprises greater than 90, more preferably greater than 95, particularly greater than 98, and especially consists essentially of 100 weight % of the hard and soft polyester blocks as defined herein. Thus, the block copolyester according to the present invention may comprise small amounts of other materials (for example other than the dicarboxylic acids and diols as disclosed herein), preferably less than 10, more preferably less than 5, and especially less than 2 weight % of non-polyester materials, such as polyethers.
The block copolyester preferably has a melting point (Tm) in the range 200 to 280xc2x0 C., more preferably 210 to 265xc2x0 C., particularly 215 to 245xc2x0 C., and especially 220 to 225xc2x0 C. In a particularly preferred embodiment of the invention, the melting point of the copolyester is suitably less than 20xc2x0 C., preferably less than 15xc2x0 C., more preferably less than 10xc2x0 C., particularly less than 8xc2x0 C., and especially less than 5xc2x0 C. lower than the melting point of the hard segment. By melting point of the hard segment is meant the melting point of the isolated component of the hard segment, for example such a component having a molecular weight number average of greater than or equal to approximately 10,000. Thus, where the hard segment is formed from butylene terephthalate, the melting point of the hard segment, ie polybutylene terephthalate is 225xc2x0 C.
The block copolyester preferably has a glass transition temperature (Tg) in the range from xe2x88x9280 to xe2x88x9240xc2x0 C., more preferably xe2x88x9270 to xe2x88x9245xc2x0 C., particularly xe2x88x9265 to xe2x88x9250xc2x0 C., and especially xe2x88x9260 to xe2x88x9255xc2x0 C. In a particularly preferred embodiment of the invention, the glass transition temperature of the copolyester is suitably less than 20xc2x0 C., preferably less than 12xc2x0 C., more preferably less than 10xc2x0 C., particularly less than 7xc2x0 C., and especially less than 4xc2x0 C. higher than the glass transition temperature of the soft segment. By glass transition temperature of the soft segment is meant the glass transition temperature of the isolated component of the soft segment. Thus, where the soft segment is formed from C36 dimer fatty acid (and, for example, 1,4-butanediol), the glass transition temperature of the soft segment is xe2x88x9260xc2x0 C.
The block copolyester according to the present invention may be produced by pre-forming the hard segment, and forming the soft segment in situ in the presence of the hard segment. The aforementioned method is particularly advantageous when the same diol is used to form both the hard and soft segments, especially where the hard segments are polybutylene terephthalate, i.e. 1,4-butane diol is used to form both the hard and soft segments. Alternatively, the block copolyester may also be prepared by pre-forming both the hard and soft segments, and then reacting them together, for example via the reactive extrusion of the homopolymers of both the hard and soft segments. The resulting block copolyester may be further polymerised by solid state polymerisation (SSP) in order to increase the molecular weight of the copolyester.
The degree of blockiness can be expressed by measuring the % transesterification, as described herein, and a block copolyester according to the present invention preferably has a % transesterification of less than 75%, more preferably in the range from 15 to 65%, particularly 25 to 55%, and especially 30 to 45%.
The block copolyester suitably has a thermal stability, measured as described herein, of greater than 65% preferably greater than 75%, more preferably greater than 80%, particularly greater than 85%, and especially greater than 90%, and up to 100%, retention of elongation after heating at 150xc2x0 C. in air for 2000 hours.
The block copolyester suitably has a hydrolytic stability, measured as described herein, of greater than 65%, preferably greater than 75%, more preferably greater than 80%, particularly greater than 85%, and especially greater than 90%, and up to 100%, retention of elongation after heating in boiling water for 600 hours.
The block copolyester described herein may be used in a wide range of applications where thermoplastic elastomers are normally used, such as bearings and seals, belts, boots and bellows, coiled tubing, reinforced housing, electric cables, electric switches for appliances, and all types of automotive parts. The block copolyester is particularly suitable for use in applications where a good thermal/oxidative stability is required, such as under-the-bonnet applications in the automotive industry, like cables and constant velocity joint boots for cars. The block copolyesters according to the present invention provide improved heat stability and high melting points.